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fcb8d040e8
Instead of lengthy blurbs, switch to single-line, machine-readable standardized (https://spdx.dev) license identifiers. The Linux kernel switched long ago, so there is strong precedent. Three cases are handled: AGPL-only, Apache-only, and dual licensed. For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0), reasoning that our changes are extensive enough to apply our license. The changes we applied mechanically with a script, except to licenses/README.md. Closes #9937
83 lines
2.7 KiB
C++
83 lines
2.7 KiB
C++
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/*
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* Copyright (C) 2015-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: AGPL-3.0-or-later
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*/
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#pragma once
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#include <seastar/core/abort_source.hh>
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#include <seastar/core/sleep.hh>
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#include <seastar/core/do_with.hh>
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#include <seastar/core/future-util.hh>
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#include "seastarx.hh"
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#include <chrono>
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// Implements retry policy that exponentially increases sleep time between retries.
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class exponential_backoff_retry {
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std::chrono::milliseconds _base_sleep_time;
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std::chrono::milliseconds _sleep_time;
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std::chrono::milliseconds _max_sleep_time;
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public:
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exponential_backoff_retry(std::chrono::milliseconds base_sleep_time, std::chrono::milliseconds max_sleep_time)
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: _base_sleep_time(std::min(base_sleep_time, max_sleep_time))
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, _sleep_time(_base_sleep_time)
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, _max_sleep_time(max_sleep_time) {}
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future<> retry(abort_source& as) {
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return sleep_abortable(update_sleep_time(), as);
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}
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future<> retry() {
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return sleep(update_sleep_time());
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}
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// Return sleep time in seconds to be used for next retry.
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std::chrono::milliseconds sleep_time() const {
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return _sleep_time;
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}
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// Reset sleep time to base sleep time.
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void reset() {
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_sleep_time = _base_sleep_time;
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}
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private:
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std::chrono::milliseconds update_sleep_time() {
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// calculating sleep time seconds for the next retry.
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return std::exchange(_sleep_time, std::min(_sleep_time * 2, _max_sleep_time));
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}
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template <typename T>
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struct retry_type_helper;
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template <typename T>
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struct retry_type_helper<future<std::optional<T>>> {
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using optional_type = std::optional<T>;
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using future_type = future<optional_type>;
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};
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public:
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template<typename Func>
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static auto do_until_value(std::chrono::milliseconds base_sleep_time, std::chrono::milliseconds max_sleep_time, seastar::abort_source& as, Func f) {
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using type_helper = retry_type_helper<std::result_of_t<Func()>>;
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auto r = exponential_backoff_retry(base_sleep_time, max_sleep_time);
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return seastar::do_with(std::move(r), [&as, f = std::move(f)] (exponential_backoff_retry& r) mutable {
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return seastar::repeat_until_value([&r, &as, f = std::move(f)] () mutable {
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return f().then([&] (auto&& opt) -> typename type_helper::future_type {
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if (opt) {
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return make_ready_future<typename type_helper::optional_type>(std::move(opt));
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}
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return r.retry(as).then([] () -> typename type_helper::optional_type {
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return { };
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});
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});
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});
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});
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}
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};
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